Pilot-type selector valve for hydraulic motors



PILOT-TYPE SELECTOR VALVE FOR HYDRAULIC MOTORS Filed Oct. 18, 1954 Nov.1, 1960 A. A. MEDDOCK 2 Sheets-Sheet 1 wimif w.

Q one INVENTOR. A. A. MEDDOCK ATTORiN EY Nov. 1, 1960 A. A. MEDDOCK2,958,339

PILOTTYPE SELECTOR VALVE FOR HYDRAULIC MOTORS IN VEN TOR. AA. MEDDOCKsZLLQW ATTORNEY United States Patent PILOT-TYPE SELECTOR VALVE FORHYDRAULIC MOTORS Alvin A. Meddock, Van Nuys, Califi, assignor to TheBendix Corporation, a corporation of Delaware Filed Oct. 18, 1954, Ser.No. 462,744

Claims. (Cl. 137-621) This invention is a continuation-in-part of myco-pending application 318,479, filed November 3, 1952, and nowabandoned, and relates to selector valves for controlling hydraulicmotor cylinders and is adapted for, although not limited to, hydrauliclift systems for tractors.

An object of the invention is to reduce the cost of manufacture ofselector valves of the shuttle piston type Without impairing theirefliciency.

Another object is to provide a selector valve that automaticallysupplies a limited back pressure to the motor cylinder to prevent avacuum being drawn therein by load forces.

A further object of invention is to provide in a selector valve of theshuttle piston type which may be used in a hydraulic lift system fortractors, manually controllable means for controlling the speed of theextension stroke of a tractor mounted cylinder.

Another object of invention is to provide in a selector valve of theshuttle piston type which may be used in a hydraulic lift system fortractors, manually controlled means for controlling the speed of theextension stroke of a tractor mounted cylinder and remote tool cylinderconnected in series with the tractor mounted cylinder.

Another object is to provide a relatively simple, inexpensive andreliable pilot-type valve construction.

A conventional pilot valve of the shuttle type comprises a valvecylinder having a central pressure chamber, a pair of return chambersspaced on opposite sides of the pressure chamber and a pair of controlports rmpectively intermediate the pressure and return ports, incombination with a shuttle piston having a pair of lands which inneutral position block the control ports from both the pressure andreturn chambers. When the shuttle piston is moved in either directionaway from neutral, the lands simultaneously uncover the control ports toconnect one to the pressure chamber and the other to the return chamber.For sensitive control in a system employing automatic follow-up, thelands must be only slightly longer than the control ports they cover sothat only a relatively slight movement of the piston covers or uncoversthe ports. This necessitates very accurate machining of the lands, whichis expensive.

The extent of accurate machining required is reduced in accordance withthe present invention by slightly reducing the diameters of the outerend portions of the piston lands so that in neutral position of thepiston the reduced portions thereof lap the control ports and provide arestricted leakage path between the control ports and the returnchambers. With this construction it is not necessary to accurately spacethe outer edges of the lands from the inner edges, since either controlport is already connected to return chamber at the instant the othercontrol port is connected to pressure. The arrangement entails a slightwastage of pressure fluid into the return chamber from the control portconnected to the pressure chamber while the valve is opening, but thisis inconsequential in practice.

It is common in many hydraulic systems to connect two 2,958,339 PatentedNov. 1, 1960 motor cylinders in series with each other to a singlecontrol valve. When the valve is in neutral, the motor cylinders aretheoretically hydraulically locked against movement. However, underheavy load, and as a result of unavoidable leakage in the valve, one ofthe motors may creep in such direction as to apply suction to one end ofthe other cylinder and the frictional resistance to movement in thelatter cylinder may cause a vacuum to be drawn between the two motors.Further in accordance with the invention I prevent such action byapplying a constant low pressure through a check valve to the other endof the said other cylinder suflicient to overcome its friction andprevent a vacuum being produced in the one end in response to suctionapplied thereto. The desired low pressure is produced by a relief valvein the return passage of the valve, which low pressure is also used toenable pilot operation of the main valve under all conditions.

A full understanding of the invention may be had from the followingdetailed description with reference to the drawing, in which:

Figure l is a schematic view of a hydraulic system incorporating a valvein accordance with the present in vention, the valve being shown inlongitudinal section;

Figure 2 is an enlarged detailed section showing the relative dimensionsof the lands and ports of the pilot valve; and

Figure 3 is a schematic view of the hydraulic system similar to Figure1, showing manually adjustable speed control means associated with thevalve structure.

Referring to Figure l, the system therein disclosed comprises a pilottype valve 10' having a pressure passage 11 connected to the output of apump 12 which draws fluid from a reservoir 13. The valve 10 also has areturn port 14 which is connected to the reservoir 13 and a pair ofmotor ports 15 and 16 which are connected to two motor cylinders 17 and18 respectively. As shown, the motor port 15 is connected to the leftend of the motor cylinder 17 and the motor port 16 is connected to theright end of the motor cylinder 18. The rightend of the motor cylinder17 is connected to the left end of the motor cylinder 18 by a conduit 19so that the two motor cylinders are connected in series relation betweenthe motor ports 15 and 16.

In the present instance, the motor cylinder 18 is the working cylinder,having a piston 18a which has a piston rod 18b which may be connected tothe load to be moved. The other motor cylinder 17 is used as a controlcylinder to stop the motors when they have moved into a positioncorresponding to the setting of a control handle 21. To this end thepiston rod 17b of the motor cylinder 17 is connected to the upper end ofa lever 23 which is connected intermediate its ends to the piston rod 25of the valve 10 and is connected at its lower end by a link 26 to thelower end of the control handle or lever 21. Movement of the handle 21into a new position causes the lever 23 to fulcrum about its point ofconnection to the piston rod 17b and to move the valve rod 25 indirection to supply fluid to move the motors 17 and 18 in a desireddirection. This movement of the motor piston rod 17b causes the lever 23to fulcrum about its lower end and move the valve rod 25 back intoneutral position when the motors have reached a position correspondingto the last setting of the handle 21.

The valve 10 is of the open center type in which fluid from the pump 12is bypassed through the valve back to return when the valve is inneutral position. However, to prevent the development of excessivepressures during any phase of the operation, it is customary to connecta relief valve 28 across the pump 12.

The valve 10 comprises a body defining a main cylinder 30 containing areciprocable main piston 31 which is normally maintained in a centralneutral position by a pair of centering springs 32 and 33 at oppositeends thereof. The spring 32 is interposed between an outer closure:member 34 for the cylinder 30 and a washer 35 which bears against oneend of the piston 31 and also bears against a flange 36 when the pistonis in neutral position, thereby limiting the extent to which the pistoncan be moved by the spring 32. The spring 33 is similarly interposedbetween the other outer closure member 37 and a washer 38 which bearsagainst the right end of the piston 31 and against a shoulder 39 in thevalve body. The main cylinder 30 has a first annular motor port 30aconnected to the motor port 15, a second annular pressure port 30bconnected to the pressure passage 11, a third annular return port 30cconnected to the return port 14, and a fourth annular motor port 30dconnected to the motor port 16.

The main piston 31 is hollow, having a central bore 31a communicatingwith a counterbore 31b at the left end and with a counterbore 310 at theright end. The outer end of the counterbore 31b is closed by a closuremember 40 and the right or outer end of the counter bore 31c is closedby a closure member 41. The outer cylindrical surface of the piston 31consists of lands separated by recesses including a first annular recess31g, a second annular recess 31d, a third annular recess 31e and afourth annular recess 31 The first piston recess 31g is connected bypassages through the piston with the counterbore 31b, the second pistonrecess 31d is similarly connected to the center bore 31a, and the thirdrecess 31a is connected to the right hand counterbore 310.

The valve body also defines a pilot cylinder 50 containing a pilotpiston 51 which is connected at its left end to the piston rod 25previously mentioned. The pilot cylinder 50 is provided with two spacedannular control ports 50a and 50b respectively which are connected tothe left and the right ends respectively of the main cylinder 30. Thecenter portion of the cylinder 50 is connected to the pressure passage11 and the outer end portions of the cylinder 50 are connected bypassages 53 to the annular return port 300 in the main cylinder, whichas previously indicated is connected directly to the return port 14.

The pilot piston 51 is provided with a pair of spaced lands 51a and 51b,which cooperate with the pilot cylinder control ports 50a and 50brespectively, and is prothe pilot cylinder but do not seal therewith. Ahelical spring 56 is shown compressed between the right end of the pilotpiston 51 and the right end of the pilot cylinder 50 to take up lostmotion in the linkage including the handle 21 and lever 23 and insureimmediate response of the piston to movement of the control handle 21 orof the motor piston rod 17b.

The apparatus functions as follows:

Normally the main piston 31 is maintained in neutral position by thecentering springs 32 and 33, and the pilot piston 51 is in centerposition, as shown, in which the lands 51a and 51b block the controlports 50a and ttb respectively from the high pressure chamber definedwithin the pilot cylinder 50 between the two lands 51a and 51b. Underthe condition described, the motor passage 15 is connected only to thefirst piston recess 31g and thence to the counterbore 31b. Thiscounterbore 31b is isolated from the centerbore 31a by a check valveconsisting of a poppet ball 60 which is urged against the left end ofthe center bore 31a by a light helical compression spring 61. This checkpoppet 60 prevents any flow of fluid from the motor port 15 into thevalve. The other motor port 16 is blocked, since the fourth pistonrecess 31f is directly juxtaposed thereto. Therefore both of the linesleading to the motors 17 and 18 are blocked and the motors will be heldin the position to which 'vided with guide surfaces 52a and 5211 thatbear against motor pistons.

they were last moved, disregarding unavoidable leakage.

At this time pressure fiuid delivered by the pump 12 to the pressurepassage 11 enters the center bore 31a of the main piston through thesecond cylinder port 30b and second piston recess 31d and is dischargedtherefrom past a pressure reducing valve into the right counterbore 310which is connected to the return port 36c in the main cylinder in allpositions of the piston. The pressure reducing valve is shown asconsisting of a ball poppet 62 urged against the right end of the centerbore 31a by a spring 63 which is relatively stiff as compared to thespring 61, and is so designed as to require an appreciable pressuredrop, say 25 to 50 p.s.i., in order to open the poppet 62. The pressurereducing valve therefore functions to maintain a certain minimumpressure in the pressure passage 11 even when the valve is in neutralposition, so as to permit control of the main valve by the pilot valveat all times. It is to be understood that in a system in which the valve62 would maintain a pressure of 25 to S0 p.s.i. in the pressure passage11, the total pressure output of the pump might be in the neighborhoodof 1000 pounds and the minimum pressure maintained by the valve would beonly sufficient to positively overcome the frictional resistance tomovements of the This minimum pressure is applied past the check poppet60 to the motor port 15 and thence to the left end of the motor 17, butordinarily it would produce no movement of either motor because theother motor port 16 connected to the other end of the motor circuit ispositively blocked in neutral position of the valve. 7

' Let it be assumed now that there is a heavy load connected to themotor piston rod 18b urging it to the right and that as a result of thisforce there is some leakage of fluid into the motor port 16 and past theclearances between the main cylinder and the main piston lands,permitting the motor piston 18a to creep to the right. This movement ofthe piston 18a creates suction in the left end of the motor cylinder 18and in the right end of the motor cylinder 17 which may be insufficientto overcome the frictional resistance of the motor piston 17a. Ifspecial means were not provided to prevent it, this suction might draw avacuum in the right end of the motor cylinder 17 and the left end of thecylinder 18 which would interfere with the normal operation of thesystem. However, in accordance with the present invention the minimumpressure of say from 25 to 50 p.s.i. produced in the center bore 31a bythe pressure reducing valve 62 is applied past the check ball 64 intothe motor port .15 and thence to the left end of the motor cylinder 17.This pressure is sufiicient to force the motor piston 17a to follow anycreeping movement of the motor piston 18a and thereby prevent theproduction of a vacuum in the system. The resultant movement of themotor piston 17a with the motor piston 18a will actuate the pilot valve(in a manner which will become apparent from the description to follow)and cause the restoration of the motor pistons to their originalposition.

Now assume that it is desired to cause the motor pistons 17a and 18a tomove a predetermined distance to the right. This is accomplished byshifting the control handle 21 a predetermined distance to the right,causing a corresponding leftward movement of the lower end of the lever23, which at this time fulcrums about its upper end and carries thepilot piston rod 25 to the left. Corresponding movement of the pilotpiston 51a to the left causes the land 51a to connect the pressurechamber in the pilot cylinder intermediate the lands 51a and 51b to thecontrol port 59a thereby admitting low pressure fluid (at 25 to 50p.s.i.) to the left end of the main cylinder 30 which moves the mainpiston 31 into its rightmost position, compressing the centering spring33 in so. doing... As the main piston 31 moves into its rightmostposition, fluid to the right of shoulder is exhausted into the controlport 50b and then to passage 53 past land 51b and then to the reservoirthrough return port 14. In the right end position of the main piston 31,the first piston recess 31g bridges and interconnects the ports 30a and30b respectively, thereby applying pressure fluid directly through themotor port 15 t0 the left end of the motor cylinder 17. At the same timethe second piston recess 31d is carried out of registration with thecylinder pressure port 30b so that the pressure fluid can no longer bebypassed past the pressure reducing valve 62 to the return line.However, the second piston recess 31d is carried into lapping relationwith the motor port 30d so that fluid can be returned through the motorport 16, the motor port 30d, the piston recess 31d, and the piston bore31a past the valve 62 to the return line. The motor pistons aretherefore moved to the right, and the movement of the motor piston rod17b shifts the upper end of the lever 23 about its lower end as afulcrum thereby moving the pilot piston 51 to the right into neutralposition, this position being reached when the motor pistons havetraveled a distance corresponding to the last setting of the controlhandle 21, whereupon the piston land 51a again blocks flow from thepressure passage to the left end of the main cylinder, and permitsreturn of the main piston to neutral by the centering spring 33. Owingto follow up movement by the lever 23, the pilot valve 51 is movedrightwardly for restoration to its neutral position thereby openingcommunication of control port 50a to passage 53 allowing fluid to beexhausted from the cylinder 30 at the lefthand end of the main piston 31and allowing the piston to move leftwardly to its neutral position.

When the main piston 31 is in its right hand position, it will be seenthat pressure from the pressure passage 11 is communicated to the backor spring side of the check valve 60 while the return flow from motor 18is communicated through motor port 30d to the central bore 31acommunicating with the inlet side of the check valve 60. If the weight,etc., tending to move the piston rod 18b causes piston 13a to be movedfaster than pump 12 can supply fluid to the motor 17, check valve 60will open to permit flow from the motor 18 to proceed directly to themotor 17, thereby preventing cavitation in the system. In this respect,back pressure valve 62 is important inasmuch as it helps to maintain theentire system above atmospheric pressure.

Movement of the control handle 21 to the left causes the motor pistonsto move to the left in the following manner: The leftward movement ofthe handle 21 causes the pilot piston 51 to move to the right to admitpressure fluid past the land 51b to the right end of the main cylinder30 and thereby move the main piston 31 into its left end position,compressing the centering spring 32 in so doing. In its left endposition, the main piston recess 31 connects the motor passage 16 to thepressure port 3%, thereby admitting pressure fluid to the right end ofthe motor cylinder 18. At the same time, the second motor piston recess31d is moved into communication with the motor port 30a permittingreturn of fluid through the motor port 15 and the piston recess 31d tothe center bore 31a and thence past the pressure reducing valve 62 tothe return line.

As clearly seen in Figure 3, a manually adjustable speed controlassembly 100 may be incorporated in the control valve to limit thetravel of the main piston 31 and the speed of the extension stroke ofthe piston of cylinder 18 and a contraction stroke of the piston ofcylinder 17.

The actuation and functioning of the valve is substantially the same asin the description relating to Figure l. The valve 10 includes at end102 an extending portion 104 in axial alignment with the main cylinder30. The extending portion 104 includes therein a central tapped boreportion 106 terminating in an enlarged counterb'ored portion 108adjacent the closure member 37. Reciprocably supportedin thecounterbored portion 108 is an adjustable stop member 110 which can beurged into contact with closure member 37 to move said member 37 towardthe main piston 31. Movement of stop member 110 is controlled by theadjustable screw member 112, threadedly supported in the tapped portion106. The screw member 112 has a knurled handle 114 secured on itsexternal end in any suitable manner. Suitable seal means 116, such as aring seal, is provided on the outer periphery of stop member 110 toprevent fluid leakage out through the tapped bore 106.

The speed control operates as follows: as previously mentioned the valve10 is actuated and functions in a manner similar to the structure ofFigure 1 however, when it is desirable to control the speed of theextension of the piston 1712 or 18b, the adjustable stop member 110 ismoved inwardly, moving closure member 37 toward the piston 31 and thusreducing the length of travel of piston 31 toward the closure member 37.The reduction of travel of piston 31 will alter the relationship of theexternal recesses 31g, 31d, 31e, 31 on the outer surface of piston 31relative to the motor ports 30a and 30d, pressure port 30b, and returnport 300. Assuming the above mentioned adjustment has been made,movement of the handle 21 to the right will result in pistons 17a and18a moving toward the right on an extension stroke, in the case ofpiston 18a, and a contraction stroke in the case of piston 17a and thepassage of fluid through the valve will be as described relative toFigure 1. Closure member 37 limits the rightward movement of piston 31and the opening between motor port 30d and annular recess 31d isreduced, i.e. the land between recesses 31d and 31;, does not move asfar to the right, as when the piston is permitted maximum travel to theright, as seen for example in Figure 1. With the impeded flow of exhaustfluid between motor port 30d and recess 31d, the speed of rightwardtravel of pistons 18a and 17a is diminished accordingly, since the speedat which the fluid can be exhausted from the right end of cylinders 18and 17 controls the speed of the extension stroke of the respectivepistons contained therein.

In the event cylinder 18 is eliminated in a given system wherein only atractor mounted cylinder is used, and line 19 is connected to motor port16, the valve structure will operate in the same manner as just.described.

It has been previously mentioned that a defect of pilottype selectorvalves as heretofore manufactured has been that the lands on the pilotpiston had to be manufactured with extreme accuracy to cause connectionof one end of the main cylinder to the return line simultaneously withconnection of the other end of the maincylinder to the pressure line. Ifsuch accuracy was not obtained, the main valve responded slowly tomovement of the pilot piston. Thus if the pilot piston admitted pressurefluid to one end of the main cylinder before it connected the other endof the main cylinder to return, then the main piston would not moveuntil the return connection was completed.

In accordance with the present invention this defect is eliminated byreducing the diameter of the left end of the land 51a and the right endof the land 51b, which are the ends of the lands that control the flowof fluid from the main cylinder to return. The reduced sections of thelands 51a and 51b are indicated at 70 in Figure 1, and Figure 2 showsapproximate dimensions that may be employed.

It will be observed from Figure 2 that the right edge of the land 51aoverlaps the right edge of the control port 50a .012 inch and that theleft edge of the control port 50a is approximately at the mid point ofthe reduced section 70 of the land 51a and that the total length of thereduced-section 70 may be .050 inch. The radius.

of the reduced section 70 is shown as .004 inch less than the radius ofthe main portion of the land 51a. Some leakage from port 50a directlyinto the return line is occasioned by this clearance, but as soon as thepilot valve has traveled approximately .020 inch from neutral positionthe main portion of the land seals the path to return and the leakageoccurs only during a small part of the opening movement of the valve.However, at the time the right edge of the land 51a clears the rightedge of the control port 5011 during leftward movement of the pilotpiston 51, the reduced section 70 at the right end of the land 51b isalready providing a path for return fluid from the right end of the maincylinder 30, so that the main piston 31 begins to move as soon as theright edge of land 51a clears the edge of the control port 50a. Thedistance between the right edge of the land 51a and the left edge of theland 51b must still be accurately determined by careful machining, butsince the outer edges of the two lands 51a and 51b do not requireaccurate positioning, the total cost of production of the piston issubstantially reduced without undesirable results in use.

The invention is disclosed in connection with a double acting system inwhich the motors 17 and 18 are positively hydraulically actuated in bothdirections. However, it is also applicable to single acting systems inwhich the motor load acts only in one direction. Thus if the load onmotor piston rod 18b always urged it to the left, the motor passage 16of the valve and the motor port 30d and piston recess 31 could beeliminated, and the right end of motor cylinder 18 vented to atmosphere,thereby making the system single acting.

Although for the purpose of explaining the invention, a particularembodiment thereof has been shown and described, obvious modificationswill occur to a person skilled in the art, and I do not desire to belimited to the exact details shown and described.

I claim:

1. A control valve comprising a housing having a valve chamber thereinprovided with a motor port, a pressure port, and an exhaust port in theside walls thereof; a valve member slidably engaging the side walls ofsaid chamber and movable between a first, an intermediate, and a thirdposition; check valve means in said valve member constructed andarranged to permit flow therethrough in a first direction, said valvemember having flow passages therein located and arranged to connect saidpressure port with said motor port through said check valve means whenin its intermediate position, to connect said motor port to said exhaustport when in its first position, and to connect said pressure port tosaid motor port by-passing said check valve means when in its thirdposition, and means associated with said control valve for providing apredetermined back pressure to said check valve means when said valvemember is in its intermediate position.

2. A control valve comprising a housing having a valve chamber thereinprovided with a pair of motor ports, a pressure port, and an exhaustport in the side Walls thereof, a valve member slidably engaging theside walls of said valve chamber and movable between a first, anintermediate, and a third position, check valve means in said valvemember constructed and arranged to permit flow therethrough in a firstdirection, back pressure valve means in said valve member having itsdischarge ported to be in communication with said eX- haust port in allthree positions of said valve member; and said valve member having flowpassages therein located and arranged to connect said pressure port withsaid back pressure valve means and at the same time permit flow throughsaid check valve means to one of said motor ports when said valve memberis in its intermediate position, to connect said one motor port withsaid back pressure valve means by-passing said check valve means whileconnecting said pressure port 8 directly with the other motor port whensaid valve member is in its first position, and to connect said pressureport to said one of said motor ports lay-passing said check valve meanswhile connecting the other of said motor ports to said back pressurevalve means when said valve member is in its third position.

3. In a valve of the type having a housing provided with a chamber whoseside walls slidably receive a valve member movable between first,intermediate and third positions; a first pair of cooperating portsindividual ones of which are positioned in said side walls and valvemember respectively and which substantially align with one another whensaid valve member is in its intermediate position, a second pair ofcooperating ports individual ones of which are positioned in said sidewalls and valve member respectively and which substantially align withone another when said valve member is in its intermediate position, saidfirst and second pairs being spaced apart from each other; a firstpassageway in said valve member communicating the valve member ports ofsaid first and second pairs; check valve means in said passagewaypreventing flow from said first pair to said second pair of ports; and asecond passageway portions of which are located in said valve member andsaid housing and which communicates said valve member port of saidsecond pair with a return connection in said housing for all threepositions of said valve member; said ports being so located and arrangedthat with the valve member in its first position said ports of saidsecond pair are moved out of communication and said valve member port ofsaid second pair communicates with the housing port of said first pair,and with the valve member in its third position said ports of saidsecond pair are moved out of communication with each other and the valvemember port of said first pair communicates the housing ports of saidfirst and second pairs.

4. In a valve of the type having a housing provided with a chamber whoseside walls slidably receive a valve member movable between first,intermediate and third positions; first, second, third and fourth pairsof spaced cooperating valve ports, one port of each pair beingpositioned in the side walls of said chamber and the other port of eachpair being positioned in said valve member, the ports of each pair beingpositioned to communicate with each other when said valve member is inits intermediate position; said valve member having a passagewaycommunicating with its first, second and fourth ports; check valve meansin said passageway constructed and arranged to prevent back-flow fromthe valve member port of said first pair to the valve member port ofsaid second pair; said ports being located and arranged such that withthe valve member in its first position thevalve member port of saidsecond pair communicates with the Chamber port of said first pair andthe valve member port of said third pair establishes communicationbetween the valve chamber ports of said second and third pairs, suchthat with the valve member in its third position the valve member portof said first pair communicates the valve chamber ports of said firstand second pairs and the valve member port of said second paircommunicates with the valve chamber port of said third pair, and suchthat said fourth pair of ports communicate with each other for allpositions of said valve member.

5. In a valve of the type having a housing provided with a chamber whoseside walls slidably receive a valve member movable between first,intermediate and third positions; first, second, third and fourth pairsof spaced cooperating valve ports, one port of each pair beingpositioned in the side Walls of said chamber and the other port of eachpair being positioned in said valve member, the ports of each pair beingpositioned to communicate with each other when said valve member isinits intermediate position; said valve member having a passagewaycommunicating with said first, second and fourth ports; check valvemeans in said passageway constructed and arranged to prevent back-flowfrom the valve member port of said first pair to the valve member portof said second pair; said ports being located and arranged such thatwith the valve member in its first position the valve member port ofsaid second pair communicates with the chamber port of said first pairand the valve member port of said third pair establishes communicationbetween the valve chamber ports of said second and third pairs, suchthat with the valve member in its third position the valve member portof said first pair communicates the valve chamber ports of said firstand second pairs and the valve member port of said second paircommunicates with the valve chamber port of said third pair, and suchthat said fourth pair of ports communicate with each other for allpositions of said valve member; and back pressure valve means formaintaining a predetermined back pressure against fluid entering thevalve member port of said second pair.

, 6. In a control valve of the type having a housing provided with achamber whose side walls slidably receive a valve member movable betweenfirst, intermediate and third positions; first, second, third and fourthpairs of spaced cooperating valve ports, one port of each pair beingpositioned in the side walls of said chamber and the other port of eachpair being positioned in said valve member, the ports of each pair beingpositioned to communicate with each other when said valve member is inits intermediate position; said valve member having a passagewaycommunicating with said first, second and fourth ports; check valvemeans in said passageway constructed and arranged to prevent back-flowfrom the valve member port of said first pair to the valve member portof said second pair; said ports being located and arranged such thatwith the valve member in its first position the valve member port ofsaid second pair communicates with the chamber port of said first pairand the valve member port of said third pair establishes communicationbetween the valve chamber ports of said second and third pairs, suchthat with the valve member in its third position the valve member portof said first pair communicates the valve chamber ports of said firstand second pairs and the valve member port of said second paircommunicates with the valve chamber port of said third pair, and suchthat said fourth pair of ports communicate with each other for allpositions of said valve member; back pressure valve means in the portionof the passageway of said valve member positioned between the valvemember ports of said second and fourth pairs for maintaining apredetermined back pressure against fluid entering the valve member portof said second pair; spring means urging said valve member toward itsintermediate position; first and second fluid pressure means adjacentopopsite ends of said valve member and adapted to force said valvemember into its third and first positions respectively; pilot valvemeans in communication with the chamber port of said second pair ofports and movable between first, intermediate, and third positions, saidpilot valve means being constructed and arranged when in its firstposition to admit pressure to said first fluid pressure means and whenin its third position to admit pressure to said second fluid pressuremeans, thereby positioning said valve member to control fluid flowbetween said pairs of ports.

7. In a valve of the type having a valve member provided with a landdividing a valve chamber into high and low pressure opposed chambers andadapted to regulate the pressure in a valve port of predetermined widthlocated in the side walls of said valve chamber, a land portion having awidth greater than the width of said valve port and having first andsecond land portions, said first land portion being located adjacent thehigh pressure opposed valve chamber and having a width smaller than thewidth of said valve port and having a uniform cross section adapted toprovide sealing engagement with the sidewalls of said chamber, saidsecond land portion being located adjacent said low pressure opposedchamber and being of reduced uniform cross section to provide arestricted flow passage adapted to communicate said low pressure opposedchamber with said valve port, said reduced uniform cross sectionextending into said valve port a distance in excess of the clearanceprovided between said reduced cross section and the side walls of saidchamber to permit said land to control the pressure in said valve portwith a minimum of movement without having the width of said landaccurately predetermined in relation to the width of said valve port.

8. In a spool valve having a chamber provided with a pair of spacedvalve ports in the side walls thereof, each of said ports having oneedge thereof adjacent a high pressure portion of said valve chamber towhich fluid is communicated at a high pressure and each of said portshaving the opposite side edge adjacent a low pressure portion of saidchamber from which fluid is conducted at a lower pressure, a valveclosure member slidable in said chamber having a pair of spaced landseach of which extends over a respective valve port when said valveclosure member is in its normal position, said lands having firstportions of uniform cross section for sealing engagement with said oneside edge of its cooperating valve port to which pressure fluid iscommunicated, said lands being spaced apart such that said first landportions just sealingly engage said high pressure portions of said valvechamber when said closure member is in its normal position, each of saidlands having a total width greater than the width of its cooperatingvalve port and including a second land portion of reduced cross sectionoverlying said opposite side edge of its cooperating valve port whensaid closure member is in its normal position, said second land portionsproviding predetermined clearance with respect to the sidewalls of saidchamber and extending into its cooperating valve port a distance greaterthan said predetermined clearance, whereby said valve closure memberwill vary the pressure in said valve ports with a minimum of closuremovement without having the width of said lands accuratelypredetermined.

9. In a valve of the type having a housing provided with a chamber whoseside walls slidably receive a valve member movable between first,intermediate and third positions; first, second, third and fourth pairsof spaced cooperating valve ports, one port of each pair beingpositioned in the side walls of said chamber and the other port of each'pair being positioned in said valve member, the ports of each pairbeing positioned to communicate with each other when said valve memberis in its intermediate position; said valve member having a passagewaycommunicating with said first, second and fourth ports; check valvemeans in said passageway constructed and arranged to prevent back-flowfrom the valve member port of said first pair to the valve member portof said second pair; said ports being located and arranged such thatwith the valve member in its first position the valve member port ofsaid second pair communicates with the chamber port of said first pairand the valve member port of said third pair establishes communicationbetween the valve chamber ports of said second and third pairs, suchthat with the valve member in its third position the valve member portof said first pair fully communicates the valve chamber ports of saidfirst and second pairs and the valve member port of said second pair isisolated from said second chamber port and just opens communication withthe valve chamber port of said third pair, and such that said fourthpair of ports communicate with each other for all positions of saidvalve member, and adjustable means for limiting movement of said valvemember from said intermediate position toward said third position tocause restricted flow through said third chamber port.

10. A valve according to claim 5 in which said valve member comprises anopen ended tubular member having counterbores at its opposite endsjoined by a center bore; closure means closing the outer ends of saidcounterbores; said check valve means comprising a poppet in one of saidcounterbores' and a relatively light spring compressed between thepoppet and the adjacent closure member for seating the poppet againstthe adjacent end of said center bore; and said pressure reducing valvecomprising a poppet in the other counterbore and a relatively stiffspring compressed between it and the adjacent closure member for seatingit against the adjacent end of said center bore; said one counterboreconnecting directly to said first valve member port, said center boreconnecting directly to said second valve member port, and said othercounterbore connecting directly to said fourth valve member port.

11. A valve as set forth in claim 4 wherein the adjustable stop means iscarried in the valve housing in axial alignment with the movable valvemember and is adjustable by an externally extending screw member inaxial alignment therewith.

12. In a valve of the type having a housing provided with a chamberwhose side walls slidably received a valve member movable between first,intermediate and third positions; said housing having first and secondmotor ports, an exhaust port, and a pressure port communieating with thesidewalls of said chamber, a check valve Which permits flow from itsfirst side to its second side, said valve member having passage meanstherein which communicates said first motor port to said exhaust portwhile communicating said second motor port to said pressure port when inits 'first position, which communicates said pressure port with saidfirst motor port when in its intermediate position, and whichcommunicates said pressure port to said first motor port and to saidsecond side of said check valve while also communicating said secondmotor port to said exhaust port and to said first side of said checkvalve when in its third position; whereby return flow from said secondmotor port may flow through said check Valve to said first motor portshould insuflicient flow be received from said pressure port tocompletely fill the motor chamber supplied by said first motor port.

13. In a valve of the type having a housing provided with a chamberwhose side walls slidably receive a valve member movable between first,intermediate and third positions, said housing having first and secondmotor ports, an exhaust port, a pressure port communicating with thesidewalls of said chamber, a check valve which permits flow from itsfirst side to its second side, said valve member having passage meanstherein which oommunicates said first motor port to said exhaust portwhile communicating said second motor port to said pressure port when inits first position, which communicates said pressure port with saidfirst motor port when in its intermediate position, and whichcommunicates said pressure port to said first motor port and to saidsecond side of said check valve while also communicating said secondmotor port to said exhaust port and to said first side of said checkvalve when in its third position, and a back pressure valve forthrottling flow out said exhaust port to hold a back pressure on saidsecond motor port and said first side of said check valve when saidvalve member is in its third position; whereby return flow from saidsecond motor port may flow through said check valve to said first motorport should insufficient flow be received from said pressure port tocompletely fill the motor chamber supplied by said first motor port.

14. In a hydraulic system: a flow-through discharge system; a backpressure valve having inlet and outlet ports, said outlet port beingconnected to said flowthrough discharge system; a control valve having apressure port, a motor port and a control member movable between anormal position wherein said pressure port is communicated to said inletof said back pressure valve and an actuating position wherein saidpressure port is communicated to said motor port while said pressureport is isolated from said inlet of said back pressure valve; springcentering means for moving said control member from said actuatingposition to said normal position; pressure differentially operated motormeans for moving said control member from said normal position to saidactuating position, said motor means being sized to overcome the forceof said spring centering means with the differential pressure developedbetween the inlet and outlet of said back pressure valve; and a pilotvalve having a normal position wherein it communicates substantiallyequal pressure to opposite sides of said pressure differentiallyoperated motor means, and a second position wherein the pressuredifierential between the dis charge or said back pressure valve and saidpressure port is communicated to said motor means in a manner to movesaid control member into its actuating position.

15. In a hydraulic system: a flow-through discharge system; a backpressure valve having inlet and outlet ports, said outlet port beingconnected to said flowthrough discharge system; a control valve having apressure port, first and second motor ports and a control mem bermovable between a normal position wherein said pressure port iscommunicated to said inlet of said back pressure valve, and an actuatingposition wherein said pressure port is communicated to said first motorport while said pressure port is isolated from said inlet of said backpressure valve and said second motor port is communicated to said backpressure valve; spring centering means for moving said control memberfrom said actuating position to said normal position; pressuredifferentially operated motor means for moving said control member fromsaid normal position to said actuating position, said motor means beingsized to overcome the force of said spring centering means with thedifferential pressure developed between the inlet and outlet of saidback pressure valve; and a pilot valve having a normal position whereinit communicates substantially equal pressure to opposite sides of saidpressure differentially operated motor means, and a second positionwherein the pressure differential between the discharge of said backpressure valve and said pressure port is communicated to said motormeans in a manner to move said control member into its actuatingposition.

References Cited in the file of this patent UNITED STATES PATENTS912,385 Kimball Feb. 16, 1909 2,321,267 Van Der Werff June 8, 19432,347,238 Bennett Apr. 25, 1944 2,362,945 Stephens Nov. 14, 19442,550,529 Carson et al. Apr. 24, 1951 2,573,943 Ziskal Nov. 6, 19512,594,664 Livers Apr. 29, 1952 2,601,990 Holzer July 1, 1952 2,614,539Ernst Oct. 21, 1952 2,655,939 Tauscher Oct. 20, 1953 2,720,755 GardinerOct. 18, 1955 2,747,612 Lee May 29, 1956 FOREIGN PATENTS 987,883 FranceApr. 18, 1951

